It is known to electrically couple multiple switching sub-converters in parallel to increase switching power converter capacity and/or to improve switching power converter performance. One type of switching power converter with multiple switching sub-converters is a “multi-phase” switching power converter, where the switching sub-converters switch out-of-phase with respect to each other. Such out-of-phase switching results in ripple current cancellation at the converter output filter and allows the multi-phase switching power converter to have a better transient response than an otherwise similar single-phase switching power converter. Examples of multi-phase switching power converters include, but are not limited to, multi-phase buck converters, multi-phase boost converters, and multi-phase buck-boost converters.
As taught in U.S. Pat. No. 6,362,986 to Schultz et al., which is incorporated herein by reference, a multi-phase switching power converter's performance can be improved by magnetically coupling the energy storage inductors of two or more phases. Such magnetic coupling results in ripple current cancellation in the inductors and increases ripple switching frequency, thereby improving converter transient response, reducing input and output filtering requirements, and/or improving converter efficiency, relative to an otherwise identical converter without magnetically coupled inductors. The inductors must be inversely magnetically coupled, however, to realize the advantages of using coupled inductors, instead of multiple discrete inductors, in the multi-phase switching power converter. Inverse magnetic coupling is characterized by current flowing through a winding from a respective switching node to a common node inducing current flowing in each other magnetically coupled winding from a respective switching node to the common node.
Two or more magnetically coupled inductors are often collectively referred to as a “coupled inductor” and have associated leakage inductance and magnetizing inductance values. Magnetizing inductance is associated with magnetic coupling between windings; thus, the larger the magnetizing inductance, the stronger the magnetic coupling between windings. Leakage inductance, on the other hand, is associated with energy storage. Thus, the larger the leakage inductance, the more energy stored in the inductor. Leakage inductance results from leakage magnetic flux, which is magnetic flux generated by current flowing through one winding of the inductor that is not coupled to the other windings of the inductor.
As taught in Schultz et al., large magnetizing inductance values are desirable to better realize the advantages of using a coupled inductor, instead of discrete inductors, in a switching power converter. Leakage inductance values, on the other hand, typically must be within a relatively small range of values. In particular, leakage inductance must be sufficiently large to prevent excessive ripple current magnitude, but not so large that converter transient response suffers. Transformers, in contrast to coupled inductors, are normally designed to minimize leakage inductance and associated energy storage, because energy storage is normally undesirable in transformers.
Coupled inductors including a row of magnetically coupled windings have been developed. For example, FIG. 1 is a perspective view of a prior art coupled inductor 100 having a length 102, a width 104, and a height 106. Coupled inductor 100 includes a magnetic core 108 including a first plate 110, a second plate 112, and a plurality of coupling teeth 114. FIG. 2 is an exploded perspective view of coupled inductor 100 showing second plate 112 separated from the remainder of coupled inductor 100. First plate 110 and second plate 112 are separated from and oppose each other in the height 106 direction. Each coupling tooth 114 is disposed between first plate 110 and second plate 112 in the height 106 direction. A respective winding 116 is wound around each coupling tooth 114, such that windings 116 are disposed in a single row in the widthwise 104 direction.
As another example, FIG. 3 is a perspective view of a prior art coupled inductor 300 having a length 302, a width 304, and a height 306. Coupled inductor 300 includes a ladder magnetic core 308 including a first rail 310 and a second rail 312 opposing each other and separated in the lengthwise 302 direction. A plurality of rungs 314 are disposed between first rail 310 and second rail 312 in the lengthwise 302 direction, and a top magnetic element 316 is disposed over rungs 314 to provide a leakage magnetic flux path between first rail 310 and second rail 312. A respective winding 318 is wound around each rung 314, such that windings 318 are disposed in a single row in the widthwise 304 direction. FIG. 4 shows coupled inductor 300 with first rail 310 and top magnetic element 316 removed from coupled inductor 300, and FIG. 5 shows a top plan view of coupled inductor 300. The dashed line in FIG. 5 delineates first rail 310 from top magnetic element 316 to help a viewer distinguish these elements of magnetic core 308. The dashed line, however, does not necessarily represent a discontinuity in magnetic core 308.